Radio frequency (RF) generators are used to drive plasma chambers for various applications such as etching, semiconductor fabrication, and flat panel displays. Industry specified frequencies for operating RF power generators include 2 MHz, 4 MHz, 8 MHz, 3.2 MHz, 13.56 MHz, 60 MHz, and 100 MHz.
Known RF generators use continuous wave (CW) single-tone narrow-band signals which fix an RF carrier frequency at a desired operating frequency. However, an input impedance of the plasma chamber as seen by the RF generator may change drastically during operation due to perturbations of the plasma. When the input impedance changes, a possibility exists for a mismatch between the input impedance of the plasma chamber and an output impedance of the RF generator. The mismatch may be so significant that reflected waves from the plasma chamber severely impact operation of the RF generator. Alternatively, the RF generator may be self-protected and designed to turn off or reduce its output power upon detecting the significant mismatch. Either of these responses by a self-protected RF generator may cause the plasma to extinguish, which is also undesirable.